Speaking about a scene in the film which recreates the Woolworth's Lunch Counter sit-in (where a white woman spits on a black student), Carey told Yahoo! Movies: "That actually happened to me.

"I know people would be in shock and not really want to believe or accept that, but it did. That right there, that was almost the deepest thing to me in the movie because I know what she went through - and it happened to be a bus as well. It was a school bus, in the face and in the same way."

The Butler centres around Cecil Gaines (Forest Whitaker), a White House employee who served under eight presidents between 1952 and 1986.

The movie is scheduled for release in the US on August 16. A UK release date is yet to be confirmed.